In recent years there has been substantial activity directed to the preparation of zeolitic aluminosilicates having higher SiO.sub.2 to Al.sub.2 O.sub.3 ratios than the previously known zeolitic aluminosilicates. Much of this activity has been in secondary treatment processes involving secondary treatment media. A review of some of the patent literature relating to this effort is instructive.
U.S. Pat. No. 3,691,099 discloses a dealuminization process where an aqueous acidic media and a water soluble salt are employed to extract framework aluminum atoms from crystalline zeolitic aluminosilicates.
U.S. Pat. No. 3,506,400 discloses a process similar to that of U.S. Pat. No. 3,691,099 except a pretreatment step is employed and an aluminum-chelating agent is employed.
U.S. Pat. No. 4,093,560 discloses a process for removing aluminum from a zeolite wherein a water-soluble acid is employed with an ammonium or alkali metal salt such that aluminum can be extracted from the zeolite by complexing. The mineral acid can be trifluoroacetic acid.
U.S. Pat. No. 3,594,331 discloses a method for increasing the thermal stability of crystalline zeolites by treating the zeolite with a dilute solution of a fluorine compound. The treatment with a fluorine compound is a fluoride treatment (column 3, line 41 et. seq.). After the fluoride treatment has been completed the zeolite (fluoride treated) incorporates 2 to 15 grams of fluoride per 10,000 grams of zeolite. The patent notes that excess fluoride actually decreases the thermal stability of the zeolite.
U.S. Pat. No. 3,933,983 discloses a fluoride treatment process similar to U.S. Pat. No. 3,594,331 except that an ion exchange step is added (see claim 1).
The dissolution of aluminum sodium fluoride (Na.sub.3 AlF.sub.6) in aqueous solution with Al.sub.2 (SO.sub.4).sub.3, Al(NO.sub.3).sub.3 and AlCl.sub.3 has been reported by F. J. Frere, J. Am. Chem. Soc., 58, 1695-7 (1936) and by A. Seidell, "Solubilities of Inorganic and Metal Organic Compounds", Vol I, 4th Ed p. 184, (1958) D. Van Nostrand Co., Inc., Princeton, N.J.
The above processes are generally directed to only the extraction or removal of aluminum from a aluminosilicate zeolite. A process directed to the removal of aluminum and insertion of SiO.sub.4 tetrahedra in the framework of the aluminosilicate is disclosed in copending U.S. Ser. No. 315,853, filed Oct. 28, 1982, now U.S. Pat. No. 4,503,023, commonly assigned and incorporated herein by reference thereto. This process inserts silicon atoms as SiO.sub.4 tetrahedra by treating an aluminosilicate having a SiO.sub.2 /Al.sub.2 O.sub.3 ratio of at least 3 with a fluoroaluminate salt in an amount of at least 0.0075 moles per 100 grams of the zeolitic aluminosilicate on an anhydrous basis, said fluorosilicate salt being in the form of an aqueous solution having a pH value within the range of 3 to about 7 and brought into contact with the zeolitic aluminosilicate at a rate sufficiently slow to preserve at least 60 percent of the crystallinity of the starting zeolitic aluminosilicate. The process relates to the preparation of numerous molecular sieves. Products prepared from zeolite Y are generally referred to in U.S. Ser. No. 315,853 as LZ-210. The final products are water washed but residual fluoride containing species generally require exhaustive wash treatment with water, ammonium acetate and boiling water.
In copending U.S. Ser. No. 509,604, filed June 30, 1983 a process is disclosed for treating fluoride-containing aluminosilicates to decrease the amount of fluoride contained therein by use of an effective amount of a solution of a soluble aluminum compound whereby the amount of insoluble fluoride compound associated with said aluminosilicate is decreased.